Modern sports boots, such as ski boots, snowboarding boots, climbing boots, boots for ice skates or in line skates, etc., usually comprise an outer shell of a relatively firm and rigid plastic material and an inner boot that can be inserted into this outer shell and consists of a comparatively softer cushioning material, where the inner boot fixes the foot relative to the outer shell, and where the cushioning material also contributes significantly to the wearing comfort by protecting the foot from cold temperatures and from developing pressure points.
Boots of this type are known, for example, from EP 0 672 363 A1. In this case, the inner boot is provided with an additional cushioning in the form of fluid filled bubbles at locations vulnerable to the development of pressure points.
EP 0 370 948 B1 describes an inner boot of relatively rigid synthetic material, lined on the inside with a synthetic material of lesser hardness. The relatively rigid synthetic material has at least one cutout of closed outline into which the synthetic material of lesser hardness can be inserted to effect superior cushioning. This softer plastic is attached by means of sewing, welding or molding.
EP 0 351 396 A2 describes an inner boot for a ski boot that consists of a support material and a foam layer with local recesses that extend over at least 30% of the inner boot surface. This is intended to prevent pressure points at particularly critical locations, e.g., the ankle region or the instep region.
EP 0 657 11 6 A1 describes an inner boot with correcting pieces arranged thereon, where said correcting pieces serve for varying the thickness of the inner boot. This is achieved with the aid of an elastic outer lining that is partially cut out and/or open and essentially consists of an inelastic material.
CH 626 793 A5 describes an inner boot for sports boots that can be cushioned by applying additional cushioning elements with the aid of Velcro fasteners.
An objective of the above described sports boot merely consists of preventing pressure points. However, another problem is fixing the inner boot relative to the outer shell. For example, the foot will be quite constricted if the outer shell is closed with relatively high closing forces by means of toothed elements, laces or other conventional elements used to fix the inner boot, and thus the foot, relative to the outer shell. This is not only uncomfortable, but also restricts the blood supply to the foot. This leads to premature muscle fatigue, premature freezing of the feet during winter sport activities and even increased adrenaline production and symptoms of stress. On the other hand, if the outer shell is only “loosely” closed with relatively little force, the inner boot is able to shift relative to the outer shell. This is undesirable for most sport activities, e.g., skiing, snowboarding, etc., because the foot is not sufficiently supported in the boot and forces can no longer be precisely transmitted from the foot to the equipment, e.g., skis or snowboard.